1. Field of the Invention
This invention relates to conductive polymers and particularly to the use of functionalized protonic acids to induce processibility of electrically conductive substituted or unsubstituted polyanilines, and to induce solubility of electrically conductive substituted or unsubstituted polyanilines in organic liquids or fluid (melt) phases of solid polymers. Other aspects of this invention relate to the resulting solutions of electrically conductive substituted or unsubstituted polyanilines in organic liquids, to methods of forming such solutions and to methods of using such solutions to form conducting polymer articles and methods of using such solutions as electrically conducting liquids. Yet other aspects relate to solid phase polymers containing these protonic acids as plasticizers and their use in forming conductive articles.
2. Prior Art
There has recently been an increased interest in the electrical conductivity and electrochemistry of polymeric systems. Recently, work has intensified with emphasis on polymers having extended conjugation in the backbone chain.
One conjugated polymer system currently under study is polyaniline. Kobayashi Tetsuhiko et al., J. Electroanal Chem., "Electrochemical Reactions Concerned With electrochromism of Polyaniline Film-Coated Electrodes," 177 (1984) 281-291, describes various experiments in which spectro electro-chemical measurement of a polyaniline film coated electrode were made. French Patent No. 1,519,729, French Patent of Addition 94,536; U.K. Patent No. 1,216,549; "Direct Current Conductivity of Polyaniline Sulfate," M. Donomedoff, F. Kautier-Cristojini, R. ReSur-vail, M. Jozefowicz, L. T. Yu, and R. Buvet, J. Chim. Phys. Physicohim. Brol., 68, 1055 (1971); "Continuous Current Conductivity of Macromolecular Materials," L. T. Yu, M. Jozefowicz, and R. Buvet, Chim. Macromol.,1,469 (1970); "Polyaniline Based Filmogenic Organic Conductive Polymers," D. LaBarre and M. Jozefowicz, C. R. Read. Sci., Ser. C, 269, 964 (1969); "Recently Discovered Properties of Semiconducting Polymers," M. Jozefowicz, L. T. Yu, J. Perichon, and R. Buvet, J. Polym. Sci., Part C, 22, 1187 (1967); "Electrochemical Properties of Polyaniline Sulfates," F. Cristojini, R. De Surville, and M. Jozefowicz, Cr. Read. Sci ., S r C, 268, 1346 (1979 ; "Electrochemical Cells Using Protolytic Organic Semiconductors," R. De Surville, M. Jozefowicz, L. T. Yu, J. Perichon, R. Buvet, Electrochem. Ditn. 13, 1451 (1968); "Oligomers and Polymers Produced by Oxidation of Aromatic Amines," R. De Surville, M. Jozefowicz, and R. Buvet, Ann. Chem. (Paris), 2,5 (1967) "Experimental Study of the Direct Current Conductivity of Macromolecular Compound," L. T. Yu, M. Borredon, M. Jozefowicz, G. Belorgey, and R. Buvet, J. Polym. Sci. Polym. Symp., 16, 2931(1967); "Conductivity and Chemical Properties of Oligomeric Polyaniline," M. Jozefowicz, L. T. Yu, G. Belorgey, and R. Buvet, J. Polym. Sci., Polym. Symp., 16, 2934 (1967); "Products of the Catalytic Oxidation of Aromatic Amines," R. De Surville, M. Jozefowicz, and R. Buvet, Ann. Chem. (Paris), 2, 149 (1967); "Conductivity and Chemical Composition of Macromolecular Semiconductors," Rev. Gen. Electr., 75 1014 (1966); "Relation Between the Chemical and Electrochemical Properties of Macromolecular Semiconductors," M. Jozefowicz and L. T. Yu, Rev. Gen. Electr., 75, 1008 (1966); "Preparation, Chemical Properties, and Electrical Conductivity of poly-N-Alkyl Anilines in the Solid State," D. Muller and M. Jozefowicz, Bull. Soc. Chem. Fr., 4087 (1972).
U.S. Pat. Nos. 3,963,498 and 4,025,463 describe oligomeric polyanilines and substituted polyanilines having not more than 8 aniline repeat units which are described as being soluble in certain organic solvents and which are described as being useful in the formation of semiconductors compositions. European Patent No. 00117717 is an apparent improvement in the compositions of U.S. Pat. Nos. 3,963,498 and 4,025,463 and states that the polyaniline can be formed into a latex composite through use of the oligomers of polyaniline and a suitable binder polymer.
High molecular weight polyaniline has emerged as one of the more promising conducting polymers, because of its excellent chemical stability combined with respectable levels of electrical conductivity of the doped or protonated material. Processing of polyaniline high polymers into useful objects and devices, however, has been problematic. Melt processing is not possible, since the polymer decomposes at temperatures below a softening or melting point. In addition, major difficulties have been encountered in attempts to dissolve the high molecular weight polymer.
Recently, it was demonstrated that polyaniline, in either the conducting emeraldine salt form or the insulating emeraldine base form, can processed from solution in certain strong acids to form useful articles (such as oriented fibers, tapes and the like). By solution processing from these strong acids, it is possible to form composites, or polyblends of polyaniline with other polymers (for example polyamides, aromatic polyamides (aramids), etc.) which are soluble in certain strong acids and thereby to make useful articles. "Electrically Conductive Fibers of Polyaniline Spun from Solutions in Concentrated Sulfuric Acid," A. Andreatta, Y. Cao, J. C. Chiang, A. J. Heeger and P. Smith, Synth. Met., 26, 383 (1988 ; "X-Ray Diffraction of Polyaniline," Y. Moon, Y. Cao, P. Smith and A. J. Heeger, Polymer Communications, 30, 196 (1989); "Influence of the Chemical Polymerization Conditions on the properties of Polyaniline," Y. Cao, A. Andreatta, A. J. Heeger and P. Smith, Polymer, 30, 2305 (1990); "Magnetic Susceptibility of Crystalline Polyaniline," C. Fite, Y. Cao and A. J. Heeger, Sol. State Commun., 70, 245 (1989); "Spectroscopy and Transient Photoconductivity of Partially Crystalline Polyaniline," S. D. Phillips, G. Yu, Y. Cao, and A. J. Heeger, Phys. Rev. B , 10702 (1989); "Spectroscopic Studies of Polyaniline in Solution and in the Solid State," Y. Cao and A. J. Heeger, Synth. Met. 32, 263, (1989); "Magnetic Susceptibility of One-Dimensional Chains in Solution," C. Fite, Y. Cao and A. J. Heeger, Solid State Commun., 71, 607 (1990); "Electrically Conductive Polyblend Fibers of Polyaniline and Poly(p-phenylene terephthalamide)," A. Andreatta, A. J. Heeger and P. Smith, Polymer Communications, 31, 275 (1990); "Polyaniline Processed From Sulfuric Acid and in Solution in Sulfuric Acid: Electrical, Optical and Magnetic Properties," Y. Cao, P. Smith and A. J. Heeger in Conjugated Polymeric Materials: Opportunities in Electronics, Opto-electronics, and Molecular Electronics, ed. J. L. Bredas and R. R. Chance (Kluwer Academic Publishers, The Netherlands, 1990).
U.S. Pat. No. 4,983,322 describes solutions and plasticized co positions of electrically conductive substituted and unsubstituted polyanilines and methods of forming such solutions or compositions and use of same to form conductive articles. The polyaniline materials were made soluble by the addition of an oxidizing agent such as FeCl.sub.3. Since the resulting compounds are charge transfer salts, highly polar solvents were required; specifically solvents were needed with dielectric constants equal to or greater than 25 and with dipole moments equal to or greater than 3.25.
Starting with the insulating emeraldine base form, polyaniline can be rendered conducting through two independent doping routes:
(i) Oxidation either electrochemically (by means of an electrochemical charge transfer reaction) or chemically (by means of chemical reaction with an appropriate oxidizing agent such as FeCl.sub.3);
(ii) Protonation through acid-base chemistry by exposure to protonic acids (for example, in aqueous environment with pH less than 2-3).
These two different routes lead to distinctly different final states. In (i), the oxidation causes a change in the total number of .pi.-electrons on the conjugated chain and thereby renders it conductive. In (ii), there is no change in the number of electrons; the material is rendered electrically conductive by protonation of the imine nitrogen sites.
In the general field of conducting polyaniline, it was believed impossible to dope a high molecular weight polyaniline to the extent that it becomes a semiconductor or conductor and thereafter dissolve or plasticize the conductive form of polyaniline in common nonpolar or weakly polar organic solvents. As used herein, the terms "to plasticize" and a "plasticized composition" refer to the process and product in which a solid polymer includes an admixed liquid or semisolid phase to an extent sufficient to render the solid polymer flexible (softened) and not brittle. The liquid or semisolid additive is known as a "plasticizer." The nature of plasticized materials is described in more detail in Harry R. Allcock and Frederick W. Lampe, Contemporary Polymer Chemistry, Prentice-Hall, Inc. Englewood Cliffs, N.J. (1981), p. 13.
In the absence of solutions or plasticized forms, comprising common nonpolar or weakly polar liquids, or otherwise processible forms, the ability to form useful conductive articles out of conductive polyaniline, or composites or polyblends of conductive polyaniline with other polymers (for example polyethylene, polypropylene, polystyrene, elastomers, poly(ethylvinylacetate), etc.) is restricted. Thus, a need exists for techniques and materials to facilitate the fabrication of shaped conductive polyaniline articles, especially articles made from bulk material (conductive polyanilines and/or composites, or polyblends of conductive polyaniline with other polymers) and films, fibers and coatings.